1. Field of the Invention
The present invention relates to a monolithic ceramic capacitor, in particular, to an improvement for providing a monolithic ceramic capacitor including thinner dielectric ceramic layers.
2. Description of the Related Art
There is a demand for monolithic ceramic capacitors having a reduced size. The size of the monolithic ceramic capacitor can be effectively reduced by reducing the thickness of dielectric ceramic layers to provide a larger capacitance. When the thickness of dielectric ceramic layers is reduced, care must be taken such that a dielectric ceramic constituting the dielectric ceramic layers provides a sufficiently high reliability, in particular, in terms of its insulation property and life characteristics.
A dielectric ceramic suitable for reducing the thickness of dielectric ceramic layers is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-20167 (Patent Document 1). Patent Document 1 discloses a dielectric ceramic that is a sinter containing mole % of oxides of Ba and Ti in terms of BaTiO3, 0.25 to mole % of oxides of Re (Re is one or more elements selected from Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Y) in terms of Re2O3, 0.2 to 1.5 mole % of oxides of Mg in terms of MgO, and 0.03 to 0.6 moles of oxides of one or more elements selected from Mn, V, and Cr in terms of Mn2O3, V2O5, and Cr2O3, respectively; and having a Ba/Ti ratio of 0.970 to 1.030.
In this composition, the presence of the element of Mn, V, or Cr enhances the insulation property of the dielectric ceramic and imparts a good life characteristic to the dielectric ceramic.
The demand for monolithic ceramic capacitors having a reduced size is becoming more stringent and there has been a demand for reduction in the thickness of dielectric ceramic layers to less than 1 μm. As the thickness of dielectric ceramic layers is reduced, an electric field applied to the dielectric ceramic layers increases. For this reason, a dielectric ceramic constituting dielectric ceramic layers needs a better insulation property and a better life characteristic to meet the above demand. However, the dielectric ceramic having a composition according to Patent Document 1 above mainly has a problem regarding the insulation property of the grain boundaries and does not have a sufficiently good life characteristic.